1. Field of the Invention
The present invention relates to a process for the preparation of cyclohexylamine and dicyclohexylamine as a mixture with one another by reaction of phenol with aniline and/or ammonia under hydrogenating conditions in the presence of a palladium catalyst. The catalyst has a support of niobic acid, tantalic acid or a mixture of niobic acid and tantalic acid or a support containing such acids.
2. Description of the Related Art
An important method for the preparation of optionally substituted cyclohexylamine or dicyclohexylamine is the reduction of the corresponding aromatic nitro compounds (Houben-Weyl, Methoden der Org. Chemie (Methods of Organic Chemistry), Volume XI/1, page 360 et seq.) to primary aromatic amines and hydrogenation of the nucleus thereof. However, the nitration often proceeds non-uniformly and therefore almost always gives isomer mixtures.
There is also the possibility of converting phenols into cyclohexanones by partial hydrogenation, and of reacting these with ammonia and hydrogen to give cyclohexylamines (German Auslegeschriften 1,124,487, German Auslegeschriften 1,298,098, German Auslegeschriften 1,144,267, U.S. Pat. No. 3,124,614, CH 463,493, German Offenlegungsschrift 2,045,882 and Houben-Weyl, loc. cit., pages 611-617).
The preparation routes mentioned require several process steps which are independent of one another, and they are therefore quite cumbersome and not particularly economical.
According to previous knowledge, one-stage direct conversion of unsubstituted phenol into cyclohexylamine using ammonia and hydrogen is achieved in the presence of ruthenium catalysts or rhodium catalysts (JP-A 40/34,677, FR 1,427,543, GB 1,031,169 and German Auslegeschrift 1,276,032). The following catalysts have been employed for the abovementioned hydrogenation of the nucleus of aniline to give cyclohexylamine: cobalt catalysts with a basic addition (GB 969,542), Raney cobalt (JP 68/03180), ruthenium catalysts (German Auslegeschrift 1,106,319), ruthenium catalysts doped with alkali metal compounds U.S. Pat. No. 3,636,108) or nickel catalysts (German Patent Specification 805,518).
Most of the processes mentioned are operated under pressure and give chiefly cyclohexylamine, alongside only a little dicyclohexylamine. The dicyclohexylamine is therefore often prepared by other processes, for example by pressure hydrogenation of diphenylamine using a ruthenium catalyst (German Auslegeschrift 1,106,319). Dicyclohexylamine is furthermore formed in the reaction of cyclohexanone with cyclohexylamine in the presence of a palladium/charcoal catalyst under a hydrogen pressure of about 4 bar (FR 1,333,692). The process of the above German Patent Specification 805,518 is chiefly directed towards the production of dicyclohexylamine, but operates with cumbersome recyclings of by-product. Dicyclohexylamine furthermore is formed in the catalytic reaction of phenol with hydrogen and ammonia (U.S. Pat. No. 3,351,661) and in the hydrogenation of a mixture of aniline and phenol (U.S. Pat. No. 2,571,016). In contrast, monocyclohexylamine is formed from phenol, ammonia and hydrogen in the presence of a noble metal applied to a support (EP 53,817); this catalyst preferably contains a basic substance and/or an element from group Ib or IIb of the periodic table of the elements (Mendeleev). Aniline is obtained from phenol and ammonia in the presence of hydrogen using a palladium/cobalt catalyst on an aluminium spinel (EP 53,696).
The catalysts of the processes mentioned have an unsatisfactory service life; moreover, sometimes considerable amounts of cyclohexane are formed as a useless waste product. There was therefore the desire to develop a process which can be used on an industrial scale, in which the loss due to the formation of cyclohexane is suppressed and the service life of the catalyst used is improved. There was furthermore the desire for a process in which both cyclohexylamine and dicyclohexylamine are formed, the amount of which can be adjusted variably according to the demand for these substances.